The present disclosure generally relates to subterranean wellbore operations and equipment and, more specifically, to mechanisms for transferring hydraulic control from a primary safety valve to an insert safety valve.
Subsurface safety valves (SSSVs) are well known in the oil and gas industry and provide one of many failsafe mechanisms to prevent the uncontrolled release of wellbore fluids should a wellbore system experience a loss in containment. Typically, subsurface safety valves comprise a portion of a tubing string set in place during completion of a wellbore. Although a number of design variations are possible for subsurface safety valves, the vast majority are flapper-type valves that open and close in response to longitudinal movement of a flow tube. Since subsurface safety valves provide a failsafe mechanism, the default positioning of the flapper is usually closed in order to minimize the potential for inadvertent release of wellbore fluids. The flapper can be opened through various means of control from the earth's surface in order to provide a flow pathway for production to occur.
In many instances, the flow tube can be regulated from the earth's surface using a piston and rod assembly that may be hydraulically charged via a control line linked to a hydraulic manifold or control panel. The term “control line” will be used herein to refer to a hydraulic line configured to displace the flow tube of a subsurface safety valve downward upon pressurization, or otherwise to become further removed from the exit of a wellbore. When sufficient hydraulic pressure is conveyed to a subsurface safety valve via the control line, the piston and rod assembly forces the flow tube downward, which causes the flapper to move into its open position upon overcoming forces that tend to keep the flapper closed (e.g., biasing springs, downhole pressure, and the like). When the hydraulic pressure is removed from the control line, the flapper can return to its default, closed position. A self-closing mechanism, such as a torsion spring, can also be present to promote closure of the flapper should a loss of hydraulic pressure occur.
Some subsurface safety valves can also employ a second hydraulic line configured to counterbalance the effects of the control line and to provide an additional means of regulating the flow tube. The term “balance line” will be used herein to refer to a hydraulic line configured to displace the flow tube of a subsurface safety valve upward upon pressurization, or otherwise to become less removed from the exit of a wellbore. A balance line, when present, can operate in a similar manner to a control line and be controlled from the earth's surface.
Depending on operational considerations, a subsurface safety valve may be placed hundreds to thousands of feet downhole. During downhole placement of a subsurface safety valve, numerous opportunities exist for inadvertent damage to occur to the control line and/or the balance line, including line severance, thereby rendering the line(s) inoperative for regulating the subsurface safety valve. Line damage can also occur after a subsurface safety valve has been set in place and is in operational use. In addition to issues associated with the control line and/or the balance line, subsurface safety valves may become damaged due to corrosion or scaling and no longer function properly. In the event of hydraulic failure or related damage to a subsurface safety valve, very expensive and time-consuming workover operations may be needed to replace the non-functioning valve.